Parameters´ calculation for converter transformer in HVDC system

The converter transformer is one of the most significant components of a HVDC station. And the parameters of the converter transformer play an important role in the operation performance, technical and economic index in HVDC system. According to the valve´s surge current level, in combination with ac maximal short-circuit capacity of three phase, rated dc voltage and dc current, this paper describes the calculation of the minimal short circuit impedance of the converter transformer. Considering certain margin, the actual impedance value is obtained. Then the rated voltage of valve side and rated capacity are calculated. With the system parameters and measuring tolerances, tap changer range of converter transformer is calculated in detail. At the end of the paper, a study case is presented to verify the calculation procedure.